The Pakistan National Blindness and Visual impairment Survey is the largest and most comprehensive population-based eye survey to be conducted in Pakistan, a country of nearly 150 million people. The standardized prevalence of blindness (ICD-10, presenting <3/60 better eye from all causes) in adults and all age groups were 2.7% and 0.8%, respectively.
7 The standardized prevalence of FLV in adults and in all age groups in this survey were 1.7% and 0.8%, respectively. The ratio of blindness to FLV in Pakistan is therefore 1.6:1 in adults and 1:1 in all age groups. The blindness-to-FLV ratio in APEDS, the only other survey to use the same definitions, was 1.3:1.
5 Both surveys, finding the prevalence of blindness to be higher than the prevalence of FLV, tend to agree with an approximation “rule of thumb” suggested by experts at a WHO meeting in Hong Kong. In their report it was suggested, where data on the prevalence of FLV are not available, that 95% of the prevalence of blindness be used to estimate the prevalence of FLV.
14 Application of this rule shows that there are approximately 35 million people worldwide with FLV; however, more data are needed on the prevalence of FLV in different populations to refine this estimate.
In this study the need for services was categorized into four components based purely on distance visual acuity. In reality, the delivery of low-vision services should be needs based, multidisciplinary, and flexible, focusing on improving functional abilities. For example, an individual whose employment depends on reading small print has different requirements than does someone who is illiterate but who wants to continue farming or attending social functions. The optimal low-vision team comprises eyecare personnel, occupational therapists, adaptive technology specialists, teachers, audiologists and members of the social services and state blind societies. The mutual goal of these groups is to provide appropriate equipment together with specific orientation and training to allow the individual to maintain independence. In general, optical devices (including distance or near magnifiers, field expanders, night-vision aids) are less useful for those with poorer levels of visual function, and those affected require environmental modification (e.g., light augmentation, improving mobility). Individuals with very poor or no visual function will require rehabilitation including sensory substitution (accessing information via tactile or auditory methods). The results of this survey indicate that in Pakistan, 565,000 individuals need assessment for optical services, 735,000 need assessment for nonoptical interventions, and 424,000 need assessment for rehabilitation. As indicated earlier, the definition of FLV vision used in this article should not be the sole eligibility criteria for low-vision services, as others may also have the potential to benefit.
In our study, corneal disease accounted for more than one third of those with FLV and for just over 4 in 10 with no form vision. Comparison with APEDS data, where retinal diseases were the commonest cause, is limited, as individuals with corneal scarring considered treatable through corneal grafting were excluded from the definition in that study. In contrast corneal disease was included in our definition of FLV. Although the large proportion of corneal scarring due to trachoma, vitamin A deficiency, and trauma,
15 is avoidable, the results of treatment by corneal transplantation are often poor in these settings.
16 Furthermore in Pakistan, corneal grafting is currently not a viable option for most of those afflicted.
Although the survey was conducted with rigorous methodology and after extensive training, there are some limitations as far as FLV is concerned. For logistic reasons perimetry was conducted only on a selected subgroup which may have led to underascertainment of individuals defined as having FLV on the basis of visual field loss alone (e.g., from glaucoma or retinitis pigmentosa). In addition, visual needs cannot be assessed by distance visual acuity alone and other tests of visual function are necessary (e.g., near vision, contrast sensitivity). These were not performed, as FLV was not a primary outcome of this survey.
Although evidence exists that low-vision services improve quality of life and mental state
17 18 19 clinical trial evidence of the effectiveness of specific interventions for individuals with FLV is lacking.
20 A recent Cochrane review concluded that further research is recommended to compare different types of low-vision devices as well as to delineate patient characteristics that predict performance.
21 Designing clinical trials of low-vision interventions is challenging due to the heterogeneous nature of the causes and consequences of the conditions causing FLV, the wide range of possible interventions, the fact that interventions must be tailored to individuals’ needs, and the large number of possible outcomes (McGuire MG.
IOVS 2005;44:ARVO E-Abstract 2267). Research of this kind is urgently needed in developing counties, as findings from studies in industrialized countries may not apply in situations in which the causes and functional visual needs are quite different.
As VISION 2020 enters its second 5-year phase the provision of low-vision services and their integration into national eyecare programs is a high priority, as this has been a neglected area in the past. For example, a recent survey throughout India showed that only 48 (6.8%) of 701 eyecare institutions had a dedicated low-vision service.
22 The report concluded that low-vision services were less well developed than those for children. Lack of training and knowledge (82.3%) and of awareness (74.7%) were the perceived barriers to provision of these services.
23
In conclusion, population-based data on the prevalence and causes of untreatable visual impairment (i.e., FLV) are scarce but critically important for planning low-vision services.
24 This global information gap should be addressed as should awareness of the definition of FLV. The definition used in our study should not be regarded as a replacement for the ICD categories of blindness and visual impairment, as the ICD categories provide population-based data for planning clinical eyecare services, whereas the FLV definition provides data for providing service for the needs of the untreatably impaired.
The Pakistan government’s 5-year national plan for the prevention of blindness includes development of low-vision services at each level of service delivery in each province. At the primary level, activities include training instructors and classroom teachers in orientation and mobility and developing outreach programs. At the secondary level, the plan includes development of new low-vision clinics and resource centers, with one tertiary-level, low-vision service with early-intervention clinics in each province. Implementation should allow for the current backlog of patients requiring assessment and services, bearing in mind the anticipated doubling by 2020 of those affected. Planning also should take account of the fact that the overwhelming majority (91.5%) of people with FLV identified in this survey were illiterate, only 35.3% were of working age, and only 5.5% were both literate and of working age.